Carbon Nanotube Cathode Research Articles

An atomic/molecular-level strategy for the design of a preferred nitrogen-doped carbon nanotube cathode for Li-O2 batteries

The formation and growth of Li2O2, the primary discharge product with extremely low conductivity, will cause the passivation of the cathode and the failure or even death of Li-O2 batteries. In this paper, by means of molecular dynamics and density functional theory, we systematically investigated the morphology evolution and electron transport pathway of (Li2O2)n on the surface of nitrogen-doped carbon nanotubes (NCNTs) and the effects of the possible N configuration on the growth stability of (Li2O2)n. Our results demonstrated that the morphology of (Li2O2)n on the surface of NCNTs undergos a process from scattered small-sized clusters to film-like (axial) and toroidal (circumferential) large clusters, and finally completely surrounded the NCNTs. Compared with graphitic N1 and graphitic N2, Li2O2 tends to aggregate stably on the surface of pyridinic N3 and pyridinic N4, which can effectively reduce the capacity loss caused by Li2O2 branches and free state Li2O2. In addition, a stable gap exists between Li2O2 and NCNTs, which is attributed to the Coulomb force and van der Waals interaction. Importantly, (Li2O2)n with p-type semiconductor characteristics acts as a bridge between NCNTs, and electrons are mainly transferred along the surface of (Li2O2)n clusters. Moreover, increasing the wall number of NCNTs and using NCNT bundles were found to be beneficial to improving the deposition stability of (Li2O2)n. Notably, pyrrolic N3 with unstable structure is not recommended for practical application. These results offer general guidelines for designing highly active catalysts for Li-O2 batteries in terms of the optimization of the NCNT-based cathode, and the unique research methods also shed more light on the analysis of the discharge product behavior of other potential metal-air batteries.

A High-Performance Hybrid Biofuel Cell with a Honeycomb-Like Ti3 C2 Tx /MWCNT/AuNP Bioanode and a ZnCo2 @NCNT Cathode for Self-Powered Biosensing.

This work focusses on developing a hybrid enzyme biofuel cell-based self-powered biosensor with appreciable stability and durability using murine leukemia fusion gene fragments (tDNA) as a model analyte. The cell consists of a Ti3 C2 Tx /multiwalled carbon nanotube/gold nanoparticle/glucose oxidase bioanode and a Zn/Co-modified carbon nanotube cathode. The bioanode uniquely exhibits strong electron transfer ability and a high surface area for the loading of 1.14×10-9 molcm-2 glucose oxidase to catalyze glucose oxidation. Meanwhile, the abiotic cathode with a high oxygen reduction reaction activity negates the use of conventional bioenzymes as catalysts, which aids in extending the stability and durability of the sensing system. The biosensor offers a 0.1 fm-1nm linear range and a detection limit of 0.022fm tDNA. Additionally, the biosensor demonstrates a reproducibility of ≈4.85% and retains ≈87.42% of the initial maximal power density after a 4-week storage at 4°C, verifying a significantly improved long-term stability.

Investigation of Field Emission Properties of Multi-Emitter Carbon Nanotube Cathodes

Currently, scientists are actively studying the properties of cathodes based on various carbon materials, including carbon nanotubes. The purpose of this work is the possibility of using multi-emitter carbon nanotube cathodes for the development of field cathodes. A study was made of the field emission properties of multi-emitter cathodes based on filaments of multi-walled carbon nanotubes. For the experiments, a structure was assembled from a plurality of cathodes placed on a common base. As a result, the hypothesis of additivity of currents at low voltage was confirmed.

CNT/Cu composite cathode: A new approach to long lifetime for explosive emission cathode

Carbon nanotube (CNT) cathodes have attracted much attention in recent years due to the advantages of large field enhancement factor and low emission threshold. However, the severe ablation under intense emission makes the lifetime short and therefore limits the application in the field such as high power microwave generation. To resolve this problem, this paper proposes to mix CNTs with metals, and a novel CNT/Cu composite cathode is manufactured. The lifetime experiments under voltage of 940 kV and repetition frequency of 20 Hz demonstrate that the lifetime of the CNT/Cu composite cathode is over 3 × 105 pulses, which is much longer than that of the normal copper cathode by at least one order of magnitude. The microscopic morphology analysis reveals that the CNT micro-protrusions and whiskers should be vital for the good emission property of the new cathode.

Ultrafast laser micromachining of hard carbon/fumed silica anodes for high-performance sodium-ion capacitors

The slow sodium-ion storage kinetics of battery-type electrodes limits the performance of sodium-ion capacitors (SICs) operating under high-power conditions. In this study, ultrafast laser micromachining was utilized to accelerate the sodium-ion storage kinetics of hard carbon/fumed silica (HC/f-SiO2) anodes. The ablation process involving an ultrafast femtosecond laser source enabled three-dimensional microstructuring of hot-short HC/f-SiO2 anodes with minimal photothermal damage. The microporous structure of the HC/f-SiO2 anodes facilitated the electrolyte wetting of the active materials as well as the diffusion-limited supply of sodium-ions from the bulk electrolytes. The microstructured HC/f-SiO2 anode exhibited a sodium-ion storage capacity of 370 mAh g−1, which was higher than those of unstructured HC/f-SiO2 anodes of comparable mass (298 mAh g−1) or thickness (248 mAh g−1). In addition, the rate capability of the microstructured HC/f-SiO2 anode was superior to that of the unstructured samples. Comparative full-cell tests with oxidized single-walled carbon nanotube cathodes confirmed that micromachining of the HC/f-SiO2 anode was crucial for improving the performance of the SIC full cells. This study demonstrates that ultrafast laser micromachining of HC/f-SiO2 electrodes is a facile and reliable strategy for the development of high-performance SICs.

CuCo2S4 Nanoparticles Embedded in Carbon Nanotube Networks as Sulfur Hosts for High Performance Lithium-Sulfur Batteries.

Rational design of sulfur hosts for lithium-sulfur (Li-S) batteries is essential to address the shuttle effect and accelerate reaction kinetics. Herein, the composites of bimetallic sulfide CuCo2S4 loaded on carbon nanotubes (CNTs) are prepared by hydrothermal method. By regulating the loading of CuCo2S4 nanoparticles, it is found that when Cu2+ and CNT are prepared in a 10:1 ratio, the CuCo2S4 nanoparticles loaded on the CNT are relatively uniformly distributed, avoiding the occurrence of agglomeration, which improves the electrical conductivity and number of active sites. Through a series of electrochemical performance tests, the S/CuCo2S4-1/CNT presents a discharge specific capacity of 1021 mAh g−1 at 0.2 C after 100 cycles, showing good cycling stability. Even at 1 C, the S/CuCo2S4-1/CNT cathode delivers a discharge capacity of 627 mAh g−1 after 500 cycles. This study offers a promising strategy for the design of bimetallic sulfide-based sulfur hosts in Li-S batteries.

Ionic Liquid Gating in Perovskite Solar Cells with Fullerene/Carbon Nanotube Collectors

Metallic cathodes are one of reasons for instability in perovskite solar cells due to reaction with halogens I−, Br−, and it is desirable to have stable carbon‐based cathodes, particularly carbon nanotubes (CNTs), and transport layers such as C60/C70. In this work, we show that gating of such top CNT cathode in ionic liquid by changing gate voltage (V g) tunes the Fermi level of CNT by electrical double layer charging and causes lowering of the barrier at C60/C70 electron transport layer (ETL). Moreover, at higher V g the ions further propagate into fullerene ETL by electrochemical n‐doping, which increases dramatically performance by further raising mostly two parameters: short‐circuit current and fill factor, resulting in solar cell efficiency growth from 3% to 11%. Surprisingly, open‐circuit voltage (V oc) is not sensitive to V g in the perovskite solar cells, on the contrary to strongly enhanced V oc in ionically gated organic solar cells, where it is the main effect for ionic gating. This insensitivity of V oc to lowering of the work function of CNT electrode is a clear indication that V oc in the perovskite solar cell is determined by inner p‐i‐n junction formation in the perovskite layer itself.

Integrated pyrazine-based porous aromatic frameworks/carbon nanotube composite as cathode materials for aqueous zinc ion batteries

Aqueous zinc-ion batteries (ZIBs) have garnered intensive focus as a new generation of environmentally friendly and low-cost energy storage devices. However, the instability of the structure caused by Zn2+ insertion/extraction and slow kinetics limit its further development. Here, we proposed a rational strategy to link electroactive organic building blocks (HATN) using dual thioether bond and then in-situ polymerize it on carbon nanotube (CNT) (PAF-205/CNT). The extensive conjugated system constructed by sulfide chain and the introduction of conductive matrix can improve its conductive properties, thus increasing the utilization rate of active sites. As expected, PAF-205/CNT as the host material for zinc-ion storage shows a high initial capacity of 328.5 mA h g−1 at 50 mA g−1, a nearly 76.2 % capacity retention after 10,000 cycles at 20 A/g and a rate capacity of 89 mA h g−1 at 20 A/g. Furthermore, experimental analyses and theoretical calculation were performed to reveal the charge storage mechanism. Also, PAF-205/CNT cathode also shows good electrochemical performance in lithium-ion batteries (LIBs). Our study provides a strategy and insight for the rational design of promising organic electroactive materials for advanced metal-ion Batteries.

Electrochemical characterization of CuF2/CNTs cathode materials prepared by a coprecipitation method

Carbon nanotubes (CNTs) were proposed to improve the electrochemical performances of copper fluoride (CuF[Formula: see text] via a coprecipitation method. FE-SEM and TEM results proved that the three-dimensional conductive network was constructed by the addition of CNTs in the composites, in which some CuF2 particles attached to the outside of CNTs, and some of them grew inside the tube. According to the charge–discharge tests, with CNTs content increasing from 0 wt.% to 30 wt.%, the initial discharge capacities of CuF2 increased from 461 to 571 mAh/g, which exceeded the theoretical specific capacity of the CuF2. Moreover, the electrodes with CNTs exhibited better reversibility and rate performance than the bare electrode. CV and EIS results confirmed that the enhancements could be attributed to the inhibition of the electrochemical polarization of the electrode and the improvement on the diffusion coefficient of lithium ion in the electrode by the addition of CNTs.

Highly safe and stable Li–CO2 batteries using conducting ceramic solid electrolyte and MWCNT composite cathode

This study demonstrates a Li–CO2 battery with lithium aluminum titanium phosphate (LATP) solid electrolyte and carbon cloth-based multi-walled carbon nanotubes (MWCNTs) cathode. The LATP powder is synthesized by a facile solution-based method. The structural properties of as-prepared LATP are evaluated using X-ray diffraction (XRD) and Rietveld refinement analysis. The ionic conductivity of the LATP pellet is measured by electrochemical impedance spectroscopy (EIS) and found to be ∼5.43 × 10−4 S cm−1. Further, the morphology of the carbon cathodes with MWCNTs is examined by scanning electron microscopy (SEM). The electrochemical performance is evaluated by galvanostatic tests at a current density of 60 mA g−1 with a cut-off capacity of 600 mAh g−1 for 50 cycles. The test results signify the high performance and good cyclic stability. The Li–CO2 cell has delivered a maximum capacity of 5255 mAh g−1. Finally, to investigate further, post mortem analysis is carried out in which the discharge products are thoroughly characterized by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). This work also introduces a new geometry for Li–CO2 batteries with LATP as the solid electrolyte, enabling the development of all-solid-state batteries.

Evolution of Discharge Products on Carbon Nanotube Cathodes in Li–O2 Batteries Unraveled by Molecular Dynamics and Density Functional Theory

The performance of Li–O2 batteries (LOBs), such as capacity and overpotential, is closely related to the morphology of the discharge product. Here, the relationship between the growth behavior of Li2O2 on the surface of the carbon nanotube (CNT) cathodes and the cycle performance of LOBs was innovatively revealed based on molecular dynamics (MD) and density functional theory (DFT). Our results demonstrated that the growth of (Li2O2)n on the CNT surface mainly undergoes three stages: adhesion, branching, and connection. The stable gap between (Li2O2)n and the CNT surface was determined to be approximately 2.47 Å. Interestingly, the dense deposition thickness is positively correlated with the number of Li2O2 monomers. In addition, the formation of free Li2O2 directly induces the instability of (Li2O2)n and capacity loss. Moreover, armchair-type CNTs with larger diameters, especially single-walled CNTs and multi-walled CNTs with an odd number of tube walls were found to be more conducive to the stable growth of discharge products. Notably, (Li2O2)n is mainly composed of internal stable parts with low conductivity and amorphous components distributed on the surface with p-type semiconductor characteristics. Therefore, the regulation of the CNT structure and the preparation of catalysts to promote the conversion of Li2O2 from an ordered state to an amorphous structure play a vital role in breaking the technical bottleneck of LOBs. Our results identify the long-term controversial evolution mechanism of the product morphology, and the unique calculation ideas are also applicable to the intuitive exploration of the microscopic growth behavior of discharge products in other metal–air batteries.

Boosting Li-CO2 battery performances by creating holey structure on CNT cathodes

Li-CO2 batteries have attracted more and more attention because of their high theoretical energy density and promising CO2 capture capacity. However, irreversible formation of Li2CO3 during discharging causes a high overpotential, short cycling life, and poor rate capability. To enable Li-CO2 batteries stable and rechargeable operation, the development of high-efficiency catalysts for CO2 reduction and Li2CO3 decomposition is highly desired. Herein, holey carbon nanotubes (CNTs) are developed as the cathode catalysts for the rechargeable Li-CO2 batteries. Benefiting from abundant defects for enhancing CO2 reduction/evolution reactions and holey structures for storing more discharge products, and combining advantage of high conductivity of CNTs for rapid electron transport, the as-prepared Li-CO2 batteries with holey CNTs exhibited a low overpotential of 1.18 V at 50 mA g−1. More importantly, the batteries delivered an ultrahigh discharge capacity of 17,500 mA h g−1 and long-time stability over 1500 h at 100 mA g−1. This study unlocks new avenues to develop high-efficiency cathode catalysts for high-performance metal-CO2 batteries and beyond.

Multimodal Capturing of Polysulfides by Phosphorus-Doped Carbon Composites for Flexible High-Energy-Density Lithium-Sulfur Batteries.

The widespread adoption of Li-ion batteries is currently limited by their unstable electrochemical performance and high flammability under mechanical deformation conditions and a relatively low energy density. Herein, high-energy-density lithium-sulfur (Li-S) batteries are developed for applications in next-generation flexible electronics and electric vehicles with long cruising distances. Freestanding high-S-loading carbon nanotubes cathodes are assembled with a phosphorus (P)-doped carbon interlayer coated on commercial separators. Strategies for the active materials and structural design of both the electrodes and separators are highly efficient for immobilizing the lithium polysulfides via multimodal capturing effects; they significantly improve the electrochemical performance in terms of the redox kinetics and cycling stability. The foldable Li-S cells show stable specific capacities of 850 mAh g-1 over 100 cycles, achieving high gravimetric and volumetric energy densities of 387Wh kgcell -1 and 395Wh Lcell -1 , respectively. The Li-S cells show highly durable mechanical flexibilities under severe deformation conditions without short circuit or failure. Finally, the Li-S battery is explored as a light-weight and flexible energy storage device aboard airplane drones to ensure at least fivefold longer flight times than traditional Li-ion batteries. Nanocarbon-based S cathodes and P-doped carbon interlayers offer a promising solution for commercializing rechargeable Li-S batteries.

Synergistic electro-catalytic oxidation of ibuprofen in electro-peroxone system with flow-through carbon nanotube membrane cathode

A novel electro-peroxone membrane filtration (EPMF) system was constructed based on catalytic •OH production and enhanced mass transport with a flow-through, carbon nanotube (CNT) membrane cathode. Scanning electron microscopic and conductive atomic force microscopic characterization affirmed that the CNT membrane possessed a compact nano-porous structure with high electrical conductivity and large catalytic area. The EPMF system removed ibuprofen, a typical ozone-resistant pharmaceutical and personal care product, by 95.75 ± 1.12%, which was 3.72, 1.97 and 1.60 folds greater than those obtained in separate electrochemical filtration, and ozonation/peroxone-coupled filtration, respectively. Moreover, electron spin resonance in conjunction of quantitative •OH measurements showed that IBU degradation was mainly associated with advanced oxidation by in-situ produced •OH. The CNT cathode played a critical role in catalyzing H2O2 and O3 decomposition, which synergistically promoted •OH formation during the EPMF process. These findings provided new insights into the applicability and mechanisms of EPMF for advanced drinking water treatment.

Probing the Polysulfide Confinement in Two Different Sulfur Hosts for a Mg|S Battery Employing Operando Raman and Ex-Situ UV-Visible Spectroscopy.

We study here the Mg-polysulfide confinement inside two structurally different model porous materials, viz., toray carbon paper (TC) and multiwalled carbon nanotubes (CNT), using operando Raman and postcycling ex-situ UV-vis spectroscopy. Sulfur encapsulated inside CNT (CNT-S) and TC (TC-S) serves as S-cathodes in a rechargeable room temperature Mg|S battery. Operando Raman spectroscopy indicates the presence of higher-order Mg-polysulfides at the CNT cathode. This is due to the combination of their entrapment inside CNT and also possibly to their localization in the liquid electrolyte in the vicinity of CNT-S. This finding is directly correlated to the ex-situ UV-vis spectroscopy, which shows a lesser degree of Mg-polysulfide dissolution into the electrolyte solution. In comparison, TC-S, where sulfur is encapsulated within the open matrix formed by the nanofiber network of the carbon paper, displays poorer polysulfide confinement. The distinct differences in their abilities to confine the Mg-polysulfides are corroborated by battery performance. In the current density range (0.05-1) C, the battery with CNT-S displays much higher specific capacities, being nearly two times that of TC-S at 1 C.

Photo-Assisted Robust Anti-Interference Self-Powered Biosensing of MicroRNA Based on Pt-S Bonds and the Inorganic-Organic Hybridization Strategy.

Photo-assisted biofuel cell-based self-powered biosensors (PBFC-SPBs) possess the advantages of no need for external power supply, ease of sensing design, and simple instruments. In this work, a robust anti-interference PBFC-SPB for microRNA detection was constructed based on the Pt-S bond and the inorganic-organic hybridization strategy. The organic semiconductor [6,6]-phenyl-C61-butyric acid methylester@anthraquinone (PCBM@anthraquinone) served as an efficient light-harvesting material, and gold nanoparticle@Pt (AuNP@Pt) nanomaterials were immobilized on the surface via electrostatic adsorption for the binding of DNA. Notably, compared to Au-S bonds for DNA immobilization, the Pt-S bond exhibited better anti-interference ability. Ingeniously, cadmium sulfide quantum dots (CdS QDs) were close to the PCBM@anthraquinone substrate electrode to form sensitization structures, which was beneficial to enhance the photocurrent signal. Combining with the laccase-mimicking activity Cu2+/carbon nanotubes (Cu2+/CNTs) cathode, the PBFC-SPB for microRNA detection was achieved. Once the target existed, the identical sequence complementary microRNA would make DNA2/CdS dissociate and break away from the electrode, leading to a low signal. The linear detection range was 10 fM-100 pM, with the limit of determination of 2.4 fM (3S/N). The as-proposed strategy not only paves a new way for the design of photoelectrochemical biosensing but also opens a door for the construction of robust anti-interference bioassay for microRNA detection.

Enhanced Field Emission of Single-Wall Carbon Nanotube Cathode Prepared by Screen Printing with a Silver Paste Buffer Layer.

A high emission current with relatively low operating voltage is critical for field emission cathodes in vacuum electronic devices (VEDs). This paper studied the field emission performance of single-wall carbon nanotube (SWCNT) cold cathodes prepared by screen printing with a silver paste buffer layer. The buffer layer can both enforce the adhesion between the SWCNTs and substrate, and decrease their contact resistance, so as to increase emission current. Compared with paste mixing CNTs and screen printed cathodes, the buffer layer can avoid excessive wrapping of CNTs in the silver slurry and increase effective emission area to reduce the operating voltage. The experimental results show that the turn-on field of the screen-printed SWCNT cathodes is 0.9 V/μm, which is lower than that of electrophoretic SWCNT cathodes at 2.0 V/μm. Meanwhile, the maximum emission current of the screen-printed SWCNT cathodes reaches 5.55 mA at DC mode and reaches 10.4 mA at pulse mode, which is an order magnitude higher than that of electrophoretic SWCNTs emitters. This study also shows the application insight of small or medium-power VEDs.

Durable Zn-ion hybrid capacitors using 3D printed carbon composites.

Rechargeable Zn-ion hybrid capacitors (ZHCs) have gained considerable attention towards future energy storage applications owing to their non-flammable nature, high abundance of raw materials and remarkable energy storage performance. However, the uncontrolled growth of dendrites, interfacial corrosion of Zn anodes and limited mass loading of cathode materials, hinders their practical applicability. Herein, we demonstrate ZHCs with enhanced capacity and durability using a synergistic combination of a hybrid-ion electrolyte and a high-mass loading three-dimensionally (3D) printed graphene–carbon nanotube (Gr–C) cathode. The hybrid electrolyte composed of NaCl and ZnSO4, features higher ionic conductivity and lower pH compared with pristine ZnSO4, which enable uniform plating/stripping of Zn2+ ions on Zn anode, as demonstrated by in situ electrochemical and ex situ ToF-SIMs characterizations. Additionally, the multi-layered 3D Gr–C composite electrodes in ZHCs enable higher energy storage performance due to their porous architectures, high ion accessibility and dual-ion charge storage contributions. As a result, the 3D Gr–C//Zn cell unveiled a maximum capacity of 0.84 mA h cm−2 at 3 mA cm−2 with a high life cycle (78.7% at 20 mA cm−2) compared to the pristine electrolyte-based ZHCs (0.72 mA h cm−2 and 14.8%). The rapid rate measurements that we propose along with benchmarked energy density (0.87 mW h cm−2) and power density (31.7 mW cm−2) of hybrid electrolyte-based 3D Gr–C//Zn, pave the way for the development of dendrite-free and highly durable 3D energy storage devices.

Mass transfer analysis of boron-doped carbon nanotube cathodes for dual-electrolyte lithium-air batteries.

Dual-electrolyte Li-air batteries (LABs) have the advantages of high specific energy density and low overpotential, but the mass transfer mechanism is still unclear. Mass transfer is essential to battery performance. To improve the mass transfer capability of the positive electrode, this research studied the effect of boron (B)-doped carbon nanotubes (BC3NTs) with different amounts of defects as positive electrodes. Deep discharge results showed that the discharge voltage platform of BC3NTs was higher than that of CNTs, and the more defects, the higher the discharge voltage platform. The electrochemical impedance spectroscopy (EIS) results also showed that the more defects, the smaller the charge transfer resistance. As the discharge current density increased, the discharge voltage platform decreased gradually. Traditional molecular dynamics calculation results showed that the topological defects caused by BC3NTs reduced the Li+ and O2 diffusion energy barriers from the sidewalls from 4.5 eV to 1.65 eV and 4.94 eV to 0.11 eV, respectively. The diffusion capabilities of Li+ and O2 in BC3NTs were improved, and at the same concentration, the diffusion coefficients of Li+ and O2 increase to 3.0 × 10-9 m2 s-1 and 0.415 × 10-9 m2 s-1, respectively. The radial distribution function results showed that the larger the topological defect ring was, the greater the probability of finding Li+ and O2 near the electrode. In summary, the defects produced by BC3NTs were conducive to mass transfer, which could reduce polarization and impedance, and improve battery performance.

Artificial Solid‐Electrolyte Interphase and Bamboo‐like N‐doped Carbon Nanotube Enabled Highly Rechargeable K‐CO2 Batteries (Adv. Funct. Mater. 2/2022)

Fiber-Shaped Electrodes In article number 2105029, Bin Wang and co-workers demonstrate highly rechargeable K-CO2 batteries are with bamboo-like N-doped carbon nanotube cathodes and pre-protected K anodes decorated with an artificial solid electrolyte interphase film. The synergistic effect of efficient cathodes and durable anodes guarantees K-CO2 batteries long cycle-life, high specific capacity, and good rate capability.